Rubber containing para-phenylenediamine antiozonants



Nov. 21, 1961 E. E. sTAHLY 3,009,899

RUBBER CONTAINING PARA-PHENYLEEDIAMINE ANTIozoNANTs Filed Feb. 14, 19582 sheets-sheet 1 E. E. STAHLY Nov. 2 1, 1961 RUBBER CONTAININGPARA-PHENYLENE-DIAMINE ANTIOZONANTS Filed Feb. 14, 1958 2 Sheets-Sheet 2Y L .w o mm ma VN m0 w IOOIHQ. E V O x G d loom. H v Av comm .3| M .mIOQTO a. O N S f #AIS I l BY Qn 4% ATTORNEY United States Patent O3,009,899 RUBBER CONTAINING PARA-PHENYLENE- DIAMINE ANTIOZONANTS EldonEverett Stahly, Birmingham, Mich., assignor, by direct and mesneassignments, of three-fourths to Oliver W. Burke, Jr., Grosse Pointe,Mich., and one-fourth to Eastman Kodak Company, Rochester, NY., acorporation of New Jersey Filed Feb. 14, 1958, Ser. No. 715,339 3Claims. (Cl. 260-45.9)

The present invention relates to antiozonants for high polymers per sesubject to ozone attack, especially vulcanizable elastomers includingthe natural rubbers, synthetic elastomers such as polybutadiene, GR-Stype synthetic rubbers, other diene-vinyl copolymers such asacrylonitrile-butadiene elastomers, etc., and in addition thenon-vulcanizable elastomer-s, plastomers and resins, particularly thosewhich have residual unsaturation and aims generally to improve the same.

The present invention discloses a specific class of antiozonantsconforming to the formulation wherein R and R are selected from theclass of secondary and tertiary octyl, nonyl, decyl, undecyl and dodecylradicals and R' is a phenylene or diphenylene nucleus, These newantiozonants when incorporated finto high polymeric materials per sesubject to ozone attack protect said polymeric materials against suchozone attack. In the present invention R and R of the above mentionedformulation are preferably octyl groups including secondary and tertiaryoctyl groups, R is preferably paraphenylene, hydrocarbon substitutedphenylene or p,pdiphenylene, or hydrocarbon substituted diphenyleneradicals, and the total number of carbon atoms in the vcompound liewithin the range of 24 to 37.

PROLOGUE AND OBIECTS It is well known that many compounds possess theproperty of preserving rubber, when incorporated therein, against thesupercial hardening and crazing resulting from attack by oxygen, lightand heat. Such compounds are termed antioxidants However, as pointed outin copending U.S. application S.N. 470,401, tiled Nov. 22, 1954, thepreviously known antioxidants have not been effective to guard againstthe distinctly different effects of ozone on such materials, of whichthe generation of deep penetrating cracks is characteristic.

It has long been recognized that a solution of the problem of ozoneattack on both natural and synthetic Vrubber `goods -is greatly neededand that reduction of ozone attack or freeing of such goods from ozoneattack is of high importance. Indeed, as early as v1944 the ASTMprescribed a testing procedure for measuring ozone attack in connectionwith essentially static goods, such as refrigerator gaskets, windshieldmountings and the like.

It has more recently been recognized that when dynamically tiexed rubbergoods, such as tires, are made in the usual way with or withoutantioxidants, such articles are subject to deterioration by ozoneattack, whether in continuous or intermittent use or storage.

As above noted, attack by ozone on statically or dynamically employedrubber goods becomes apparent bly the development of penetrating crackswhich progressively become deeper with time of exposure to theatmosphere, which practically always contains ozone in trace amounts.Such cracks in tires often become sufficiently deep to cause failure.Indeed, in the case of new tires stored Ifor substantial periods, suchcracks may cause 3,009,899 Patented Nov. 21, i961 ice failure within arelatively short time after the tires are put into use. This result ofozone attack is thus quite distinct from the development of line surfacecracks, i.e., checking and crazing, attributed to oxidativedeterioration.

Ozone attack is extremely bad in areas indigent to cities such as LosAngeles, California, Where smog conditions are associated with highozone concentration, eg. from 10 parts to. 60 parts per hundred million.In Los Angeles and similar high-ozone areas so-called ozone cracks maydevelop in rubber articles such as tires, in less than a month ofstorage time. In areas suchas Detroit, Michigan, the normal ozoneconcentration in the air is less than 5 parts per hundred million, andozone cracks may not develop for several months.

In any event `ozone-cracking is recognized as one of the heretoforeimportant unsolved probl-ems in storage and use of articles containingnatural or synthetic rubber components, and the invention in saidcopending applications, and herein, aim to provide solutions for thatproblem, especially with respect to elastomers employed in dynamicusage.

For many years the rubber industry has employed chemicals such asSantoflex AW (the trade name for 6-ethoxy-2,2,4-trimethyl1,2-dihydroquinoline) in rubber articles toprotect the same against oxidation on aging. From a survey of chemicalsused to protect the products of representative manufacturers of rubbergoods, it -appears that Santoflex AW had been widely accepted and usedas one of the best materials available for that purpose. Accordingly, to`demonstrate the ozone resistance atiorded by new antiozonants, a GR-Scompound, 'containing Santoflex AW, was compared with GR-S containingother antioxidant materials to demonstrate which of such materialsseemed the most resistant to ozone attack under both static and dynamicconditions after subjecting to' heat aging conditions, and since theSantoex AW seemed to be the best of the materials so compared, thoughitself affording no adequate protection of elastomers against ozoneattack, it was used as a standard I for comparison to evaluate theimproved resistance to such attacks imparted by new and synergisticantiozonant compositions (see SN. 470,401, iiled Nov. 22; 1954). Inspite of the accepted usage of Santoilex AW in the industry it will benoted from the tables hereinafter, in which this material is used ascontrol, that relatively little protection of elastomers against ozonecracking is afforded by Santodex AW as compared to the antiozonants ofthe present invention, particularly after the samples had been heat-agedto simulate the conditions accompanying subjection of the elastomers todynamic usage.

A desirable property in case of antiozonants, as in the case of anyother additives to rubber, is inertness with respect to the curingingredients of the velastomer compound. The vulcanized compounds afterexposure to heat-aging (24 hours at 100 C. is taken as an exactingstandard herein) should still show from about 275% to 375%, or greater,elongation to be suitable for tire stocks. Original and heat-agedstress-strain properties were therefore both obtained to demonstratethat normal vulcanizations are obtainable with the antiozonantsincorporated in the elastomer compounds. For the sake of brevity, thetensile properties have been omitted from the table wherein the samplesshowed the physical properties required of the elastomer stocks. Certaincompounds including benzidine resulted in a very short stock afteraging; while protection against ozone was good, such additives causedover-curing, thus rendering them unsuitable for use in GR-S stocks formanufacture of tires and many other articles of commerce. Antiozonantsof vsaid U.S. application do accelerate the elastomer vulcanization ratebut are usable by adjustment of the conventional curing recipes inpractical application.

A further desirable property of antiozonants as well as of any otheradditives is inertness ywith respect to development of color and stainin light colored elastomer com pounds. Those additives which developdark colors are less desirable, e.g., in elastomers which are to beemployed in construction of White sidewall tires.

Thus, principal objects of the present invention are the provisions of(l) new antiozonants or `chemical com pounds `for incorporation intoelastomer and p'lastomer compositions which alone will effectivelyprotect same against ozone cracking, especially after heat-aging, (2)synergistic combinations of two or more of said new antiozonants as wellas synergistic combinations of said new antiozonants with knownantiozonants and/or antioxidants for rubber and/ or waxes which, with orwithout further synergistic combination with heavy metal soaps willelectively protect the same against ozone cracking, especially afteraging or heat-aging, without deleteriously altering the physicalproperties of the protected materials, (Si)` antiozonants which have loweffect on the vulcanization rate of the elastomers incorporating them,(4) antiozonants which are low in staining characteristics, (5) newmethods of protecting elastomers and plastomers from ozone attackcharacterized by the use of such new materials, (6) elastomer andplastomer articles including such chemicals and rendered ozone resistantthereby. Other objects and advantages of the invention will be madeapparent from more detailed description and examples of its application.

The invention of the present application resides in the new class ofantiozonants and the novel compounds of such class herein disclosed, thesynergistic combinations thereof with antioxidants and/ or waxes with orwithout the added synergism with heavy metal soaps, and methods ofapplying said new antiozonants and synergistic combinations, and theimproved products containing the same. This invention thus comprises,inter alia, (l) a class of the new and useful antiozonants for rubberconforming to the formula R-N(CH3)R-N(CH3)-R, wherein R and R" areselected from the class consisting of sec.- or tert.- octyl, nouyl,decyl, undecyl, and dodecyl, R' is p-phenylene or hydrocarbonsubstituted p-phenylene, p,pdiphenyl ene or hydrocarbon-substituteddiphenylene and the total car-bon counts of the members of the new classare within the range of 24 to 37, and (2) the previously unknown usefulchemical compounds herein disclosed, per se, as will be apparent fromthe following detailed descriptions and examples, which are to be takenas illustrative and not restrictive of the invention, the scope of whichis more particularly pointed out in the appended claims.

The term diphenylene radical as used herein includesp,p'-rnethylene-diphenylene, and p,piminodiphenylene. The preferred Rand R of the new antiozonauts of the present invention are sec.- ortert-octyl groups which encompass the following.

Secondary octyl radicals:

2-methyl-3-heptyl 2-methyl-4-heptyl 6-methyl-3-heptyl 6-methyl-2aheptyl3methyl-2heptyl 3-,methyl-4-heptyl S-methyl-S-heptyl 4-methyl-2-heptylS-methyI-Z-heptyl 4-methyl-3-heptyl 3-ethyl-2-hexyl 4-ethyl3hexyl2,2-dimethy1-3-hexyl 2,5-dimethyl-3-hexyl 5,5-dirnethyl-3-hexy14,4-dimethyl-3-hexyl 3,3-dimethyl-2-hexyl 4,4dimethyl2hexyl5,5-dimethy1-2-hexyl 4,5-dimethyl-3-hexyl 4,5-dimethyl-2-hexyl Tertiaryoctyl radicals:

l,ldimethylhexyl l-rnethyl-l-ethylpentyl l-methyl-l-propylbutyl1,1-diethyl-butyl l,2-dimethyl-l-ethylbutyl 1, l 3 ,3 -tetra-methylbutyl 1,1 ,2-trimethylpentyl 1,1 ,3-trimethylpentyl 1,1,4-trimethylpentyl1, l-dimethyl-Z-ethylbutyl 1,3-dimethyl-l-ethylbuty11,1-diisopropylethyl 1,1,2,2-tetramethylbutyl It is evident that thematerials of the present invention are monoand di-arylene diamines,which in all cases have four substituent radicals on the two aminogroups. The methyl substituents may be introduced into the parentN,N-disubstituted amines by reacting the latter with appropriatereagents as hereinafter described, or in other ways.

The methyl derivatives have now been found to have definite advantagesover the parent compound (i.e., R-NH--RNH-R), for example, advantages inScorch time and/or aging characteristics of the elastomer compounds inwhich the said antiozonant is incorporated, advantages in decreasedtendency to color or stain light colored elastomer stocks, or in othercharacteristics.

Also, while for greater antiozonant activity, it is preferred that -R bean unswbstituted or hydrocarbon swbstituted phenylene radical, within.the broaden aspects of the invention, diphenylene radicals selectedfrom the group consisting of diphenylene, methylenediphenylene andiminodiphenylene, unsubstituted and hydrocarbon substituted, may beemployed as R. The present invention demonstrates that methyl-ation ofthe parent N,N dalkyl compounds produces N,N'dimethyl-N,N'dialky1derivatives having particular advantages in antiozone activity(particularly in acrylonitrile rubbers and natural rubber), low scorchand low staining characteristics.

The appropriate incorporation of the new antiozonants gives virtualimmunity against much higher than ordinary atmospheric concentrations ofozone to elastomer compositions even when the same 4have been subjectedto radical heat-aging, thus showing that these antiozonants are capableof protecting the products for long periods of time under conditions ofdynamic usage 4as well as in static usages.

In the accompanying drawings pertaining to representative categories ofthe invention:

FIGURE l is an illustrative chart drawn to simple co-ordinates showingeffective concentrations of antiozonants of the present invention inGR-S 1500 compounds.

FIGURE 2 is an illustrative chart drawn to simple coordinates showingthe range of carbon atoms of the relative non-staining antiozonantsdisclosed and claimed herein.

PREPARATION OF ANTIOZONANTS The parent symmetrical N,Ndi-(higheralkyD-p-phenylenediamine compounds of the present invention may beprepared in a simple manner. For example one of the compounds of theabove identiiied class may be prepared by aminative reduction of2-octanone with p-phenylenediamines and hydrogen; one mole NHT-CGH-NHgplus 2 moles 2-octanone plus excess hydrogen with a hydrogenatingcatalyst, such as copper chrornite or Raney nickel, under the influenceof heat and pressure, produces the N,N-di(2octyl) derivative of thediamine, namely, 2-octyl-NH-C6H4-NH-2-octyl. The above reaction can berun with one mole of 2-octanone so that the rst product contains chiefly2-octyl-NH-C5H4-NH2, and this product can be `further treated with asecond ketone, eig., 3-octanone, 4-octanone, 5-methyl-3-heptanone, anonanone, decanone, undecanone, dodecanone and the like, to effectsubstitution in the second amino group by the corresponding alkyl group.This N,N'dialkyl-p phenylenediamine can be used as a parentdi-su-bstituted amine for preparation of N,N-dimethylN,N-(higher alkyl)derivatives as described in the third paragraph following.

An `advantageous method for preparation of N,N'disubstituted-p-phenylenediamine wherein the substituents are notidentical depends on reaction of p-nitroanilne and an octanone. Theresultant p-nitro Schii base is hydrogenated in the presence of a secondoctanone and a catalyst such as Raney nickel or copper ohromite, toproduce the corresponding p-R-NH-C6H4--NH.R.k

As an example of alkylation to produce the dimethyl substitutions of theparent diamines descriptive procedures are described for thepreparations of the monoand di-methyl substituted derivatives.

Two methyl groups may be introduced into a parent N,N'dioctylp-phenylenediamine or N-monooctyl pphenylenediamine, by the well knownmethod of heating with dimethyl sulfate at about 100 C. in anappropriate solvent such as water or an aqueous dioxane solution ofNaOH, the NaOH being regulated to maintain basicity. The methyl sulfateand NaOH `are added gradually tothe water-diamine mixture ordioxane-water-substituted pheny-lenediamine mixture at 60-65 C., twomole weights of dimethyl sulfate being employed per mole weight ofdiamine derivative. After fthe additions are completed (about 2 hrs.)the mixture is heated for about one hour and the methylated products maybe recovered by the following steps: (l) removal of water orwater-dioxane by distillation, (2) separation by decantation, ltr-ation,and the like, of the oil layer or solid material, as the case may be,from the remaining water solution, (3) distillation, or crystallizationfrom a solvent such as isopropanol, benzene, or the like.

Instead of dimethyl sulfate, a methyl halide, e. g., chioride lbromideor iodine may be employed to dimethylate 4the substitutedp-phenylenediamine derivative. For examplemethyl iodide, aqueous sodiumcarbonate and the parent phenylenediamine compound suspended therein arereuxed to disappearance of .the methyl iodide, the mixture is madestrongly alkaline, extracted with ether, benzene, or the like and theextract dried over NaOH pellets, and distilled to yield the desireddimethylated product. There are other practical methods of preparation,and the described methods are mentioned as illustrative only.

Another convenient method of preparation of N,N dimethyl-N,Nd-(higheralkyl)parylene diamine (where higher alkyl may be a secor tertradical inthe range of octyl to dodecyl inclusive) involves reaction of N,N'dialkyl-p-arylene-diamine with alkali metal alkyl to form theN,N'dialkali metal-N,N'dialkyllp-arylene diamine which is subsequentlyreacted `with a methyl halide, sultate and the like, to form thecorresponding N,Ndi methyl-N,Ndialkylparylenediamine. This procedure isparticularly adapted to the preparation of N,Ndimethyl-N,N-di-t-alkyl-p-arylenediamines; e.g., a suspensio'n of sodiumamyl (2 mole weight) was reacted with N,N di (2,4,4 trimethyl 2 pentyl)p phenylenediamine dissolved in l liter of n-pentane (2 hrs. at 30 to 35C.) The resultant suspension of disodium compound was reacted with 2mole weights of methyl iodide for 2 hours at 30-35" C.) AfterWater-washing, the pentane was evaporated to yield almost quantitativelythe desired amine oil. The ffollowing equations represent the reaction:

(The parent N,`Ndi-t-CHlq-p-phenylenediamine may be prepared from theN-sodio-t-octyl `amine and p-di-chlorobenzene.)

It has also been yfound that salts 'formed from dibasic acids andsubstituted p-phenylenediarnine antiozonants of this invention, such asoxalates and maleates thereof, can be employed as antiozonants;conversion to such dilute the antiozone activity of Ithe substituteddiamines but serves to further retard the Scorch and staining tendencyparticularly Iof the more highly branched di-alrkyl derivatives ofN,NdimethylN,N-di(higher secor tertalkyl) p-phenylene-diamines of thisinvention. Instead of preforming such said salts, the diamines anddibasic -acids can be separately incorporated into the elastomercompound to eiect the same net result as obtained by incorporating, intothe elastomer, the above said salt.

It should be noted that, in the present invention, hydrocarbonsubstituted phenylene radicals are intended to include heterocyclic(e.g., pyridyl, pyrrolidinyl, pyrrolyl, pyrrolinyl, thienyl, furyl, andthe like) substituted hydrocarbons.

GENERAL DESCRIPTION The research has shown that the new compounds arevaluable antiozonants for plastomers and resins as Well as for naturaland synthetic rubbers and are particularly useful antiozonants for tiresand like natural and synthetic products subject to ozone attack at highoperating temperatures, such as those temperatures attained by heavyduty truck tires, which temperatures may rise as high as 300 F. in use.Antiozonants are herein defined as additive agents which protect thepolymeric material, c g., natural and synthetic rubbers, againstdeterioration due to ozone attack. While serving as antiozonants, thenew compounds also serve as antioxidants, eg., the new products of thisinvention protect against deterioration of tensile properties caused byreaction of vulcanized rubber with oxygen. However, it is preferred touse the new antiozonants in larger amounts when they are used as thesole additive to protect against both oxygen and ozone. The specificclass of new compounds of this invention differ from otherwisesubstituted materials of the class of substituted arylenediamines, inthat the new compounds generally favorably eiect Scorch time and haveless tendency to stain light colored stocks.

The new antiozonants comprising Part I of this invention comprise theN,N-di(higher secand tert-alkyl)- N,N'dimethyl-p-phenylenediamines andN,N-di(higher secand tert-alkyl)-N,N'-dimethyl-p,p-diphenylene diamines(diphenylene includes the diphenylene nuclei as above dened) and whereinhigher alkyl designates C8 to C12 alkyl radicals, and the total carboncount of the antiozonant lies in the range of 2A to 37. The preferrednew antiozonants are N,N'-dimethylN,N-di(secoctyl) -pphenylenediaminesand p,p diphenylenediamines.

Thus the present invention discloses that compounds represented byR-N(CH3)R-N(CH3)R are active antiozonants, lin which R and R" arepreferably secondary octyl groups and in which R is a phenylene nucleusand the limitations on carbon count for the compound are from 24 to 37inclusive.

Specic ranges of this new class of materials are antiozonants when usedalone in amounts of about l part or more per 100 of the high polymers tobe protected and are claimed as such herein. The amounts employed forthe oxalates, maleates, furnarates, and the like derivatives of thep-phenylenediamines should be increased to some extent because of theincrease in molecular weight of the diamine resultant from conversion tosaid derivatives.

Part Il of this invention discloses synergistic combinations of theantiozonants of Part I hereof both with themselves and with antioxidantsand/ or waxes.

The antioxidants that show this synergistic eiect with the abovementioned antiozonants are members of the following classes: amines anddiamines; phenolics; hydroquinones and substituted hydroquinones;organic phosphites; aromatic esters; and thioamides.

The waxes found useful in developing synergistic antiozonant activityare the parain waxes and microcrystalline waxes and blends thereof.

This second part of the present invention thus comprises the discoverythat highly active synergistic antiozonant compositions can be preparedfrom any of the antiozonants of Part I of this invention when used inlesser amounts than above stated, and even in amounts less than l part/100 parts of the high polymer to be protected, in combination withsuitable proportions of known rubber antioxidants and/or certainthioamide antioxidants and/ or waxes.

Further this invention includes the incorporation of the newantiozonants of Parts I and Il of this invention into high polymericmaterials and into latices thereof, and the ozone resistant productstherefrom.

It is the applicants hypothesis that migration of the antiozonants ofthis invention is necessary to prevent ozone crack initiation at theair-rubber interface, and that the ability of the antiozonant to migrateis curtailed when the number of carbon atoms constituting theantiozonant is in excess of about 37, and further that when the numberof carbon atoms in said antiozonant is too small the additives migrateto the surface of the rubber compound and are lost by volatilizationfrom heating or simple aging, and thus cannot protect the product. Foreffective antiozone activity the single factor of volatility cannot beconsidered by itself, since compatibility, migratability and volatilityof the diamine antiozonant of this invention are importantinterdependent characteristics. 'Ihus certain antiozonants persistlonger in elastomer compounds than other active less volatile members ofthe present invention. Also certain antiozonants show better protectionafter aging than before aging, which could not occur if volatility ofthe antiozonant were the sole determinant. Regardless of the mechanismof protective action or the reasons therefor, it has been discovered bythe present inventor that the compounds of the present invention inwhich the carbon atom count lies within the range of 24 to 37 and inwhich there are two methyl and two higher secor tert-alkyl substituents,selected from the octyl and higher homologous radicals, one methyl oneach of N and N of the p-arylene diphenyleneamine and one said higheralkyl on each of N and N', represents the class of compounds of thisinvention which are effective as antiozonants with low Scorch and lowstaining characteristics.

To illustrate the observed critical nature of the number of carbon atomsin the alkyl substituents, and to show how such observed data tits theabove hypothesis, there is presented herewith a diagram (FIGURE 2)showing the -virtual immunity (measured by the A value procedure hereinexplained) of GR-S 1500 type synthetic rubber protected from ozonecracking by 5 parts of antiozonants represented by R(CH3)NR'-N(CH3)Rwherein R is a phenylene or diphenylene nucleus R and R are secortert-octyl radicals and when the total number of carbon atoms in theantiozonant is at least 24 and not more than 37, i.e., the limits oftotal carbons of the phenylene and diphenylene nuclei, eithersubstituted or unsubstituted, lies within the range of 6-19 for saidantiozonants wherein 18 carbons are included for the methyl and octylsubstituents on the nitrogens, when the carbon count is better thanobtained in the control compound. In this diagram an A value of 50 orless represents virtual immunity from ozone attack; while at an A valueabove 500, the samples are not considered an improvement over the usualSantoex AW antioxidant control compound simultaneously exposed to ozoneduring the period of dynamic testing. When A values are obtained thatlie from about 50 to 500 the specimens show an improvement in relationto the control compound, i.e., the antiozonants show relativeeffectiveness for ozone protection in the range above virtual immunitybut still better than the control. The line X represents the limit ofthe lowstaining and low-migration characteristics of the antiozonants ofthe present invention; the line Y represents the loss of immunity toozone attack when the ability of the antiozonants to migrate to thesurface is inadequate. The area between W and X applies to activeantiozonants which -do not have the advantages above noted with respectto stain and scorch.

Similar figures for other categories of the presently discovered newantiozonants have been drawn showing the relation of activity to carboncount (e.g., for higher alkyl groups above C8, and for diphenylenenuclei, unsubstituted and hydrocarbon substituted) but are omittedherefrom for the sake of brevity.

It has thus been found that N,Ndimethyl substituted N,N'sec andterthigher alkyl-p-phenylenediamines are likewise active antiozonantswith added advantages of improved scorch and staining properties incomparison tothe parent diamines. FIGURE l is a chart drawn for three ofthe new antiozonants demonstrating antiozonant protection of GR-S inpresence of a small amount of antioxidant added at the polymer plant(curves A, B and D). Curve C is included for comparison to show thelesser activity of the N,Ndimethyl-N,N'diprimary octyl-pphenylene inrelation to the activity of the secand tertoctyl analogues of thepresent invention, the primary derivatives not being able to impartvirtual immunity to GR-S either aged or unaged.

With the small amount of antioxidant (such as 1.25 partsphenyl-beta-naphthylamine) that is ordinarily incorporated at the rubbermanufacturing plants, substantially the same quantities of theantiozonant are required to obtain virtual immunity from ozone attack.However, the present research has shown that with larger quantities ofantioxidants present that per se have no appreciable antiozonant effect,a synergism is developed and lesser quantities of the antiozonants willthen give virtual immunity to ozone attack in static or dynamic usage.Similarly, present research has shown that up to 3 pts. of certain waxesact synergistically with the antiozonants particularly in static usages.The synergism of heavy metal salts in combination with the antiozonantsof the rst part of this invention (e.g., fatty acid salts (C3-C12),rosin acids and naphthenic acid salts of heavy metals such as lead, tin,manganese, cobalt, nickel and iron) shows that protection against ozoneattack may be obtained with as little as 0.5 part of the antiozonantmaterial, so used.

The amounts of synergistic rubber antioxidants and/or waxes used inthese synergistic combinations of Part II of this invention may varywith the specific antioxidant and/or wax, but in general are in therange of 0.5 to 7.5 parts/ parts of elastomer. Expressed in terms of theproportions of the synergistic composition, such composition thus maycomprise from 1 to 9 parts of antiozonant for rubber, from to 9 parts ofantioxidant for rubber, and from 0 to 9 parts wax, per 10 parts of thesynergistic composition.

The amine type antioxidants which, in combination with the substitutedphenylenediamines of the present invention, produce good antiozonantcompositions for elastomers and elastomer combinations, as above noted,include conventionally used amine antioxidants,amine-carbonyl-condensation products, tetrahydroquinoline derivativesand the like. More specifically the antioxidants tested for formingsynergistic antiozonant combinations with the appropriately substitutedphenylenediamines are set forth in Table A below; the synergistic waxesinclude paraiin and microcrystalline waxes and blends thereof.

The new antiozonants and/or the synergistic antioxidants and/ or waxescan be appropriately incorporated (e.g., per se if liquid, or as anemulsion if solid) into the elastomer. For example they may be added tothe elastomer latex so that the final coagulated elastomer compositioncontains the desired antiozonant or components of the synergisticantiozonant compositions of this invention, whichever is desired. Theelastomer latex may then be coagulated either in the conventionalprocedures, such as with salt-acid, glue, alum, etc., or with tin and/oriron group salts as described in copending U.S. application, S.N.523,711, led July 22, 1955, when the advantages thereof are desired.

The new antiozonants of this invention and their combinations forcombining with elastomers at the elastomer production plant can bedissolved in an appropriate solvent as, for example, a hydrocarbonsolvent like pentane, hexane, rubber solvent, etc.; an aromatic solventlike benzene, hexane, etc.; a ketone like acetone, diethyl ketone,ethylmethyl ketone, etc.; an alcohol like methanol, ethanol,isopropanol, etc. Thus, solutions ofthe new antiozonants can beproportionately added to the elastomer latex, to the coagulatedelastomer crumb, or even during the filtering of the Wet elastomercrumb, or to the crumb after tiltration.

Table A ANTIOXIDANTS SHOWING SYNERGISM WITH ANTI- OZONANTS Amines:

2,2,4-trimethyl-l,2-dihydroquinoline polymer (Age- Rite Resin D)condensation products products (e.\g.,

Rosinamine D Dodecylamine N-dimethyl-p-phenylenediaminelPolycyanohydrocarbonpolyamines of U.S. Ser. No.

566,423, tiled Dec. 30, 1955.

Phenolic:

Parazone (p-phenyl phenol) Santovar O` l(2,5-di-tert-butyl hydroquinone)Hydroquinone Antioxidant 2246 a p,p-bisphenol) Santowhite Flakes (adibutyl-phenol sulfide) Santovar A (2,5-di-tert-amylhydroquinone)Phosphites:

Triphenyl phosphite i Tri(nonylphenyl)phosphite (Polygard) Aromaticesters:

Glycerol monosalicylate ester Dipropylene glycol monosalicylate esterThioamides:

Thioacetanilide Thiocarbanilide Thioacetamide DibenzylthioureaPhenylacetothiomorpholide PREPARATION AND TESTING PROCEDURES Theprocedure employed in compounding and testing theelastomer-amino-additive compositions for the examples of Tables I, II,and III herein was as follows: as control samples cold GRS syntheticrubber (GR-S 1500 polymerized at 41 F. or GiR-S 1600 which is the sameexcept that 50 parts HAF carbon black are incorporated at the polymerplant), neoprene WHV, Hycar 1014, Butyl and natural rubber werecompounded and vulcanized according to best known commercial practicesto obtain good aging properties. Then similar compounds were preparedand vulcanized with our new antiozonants present as additives. Therecipes employed for the several elastomer compounds were as follows:

Neo-

prene Type WHV Nitrile rubber- Hycar 1014 Butyl GR-I-17 Elastomer parts)Natural rubber INGREDIENTS 1 Philblack "0 (carbon black) Thermax (carbonblack)- Statex (carbon black). Micronex W- (carbon black) Zinc oxide 5.Stearie acid 0. PBN A BLE- Neozone A Medium pine tar TP-QOB(plastieizer) 2... Dioctylphthalate (plastioizer) ParaFlux 2016 3- Oicolight oil (Sun Oil Atlantic 1115 wax Light calcined MgO Altax 4 Monex HMethyl tuads 0 Santocure 7 Sulfur Antiozonant and other additive,e

In certain cases other waxes were substituted for the Atlantic 1115 ofthe above formulae. For example Sunproof, Heliozone and Witco 127 werefound to be effective but not entirely equivalent in synergisticactivity in combination with the antiozonants of the present invention.

For neoprene and Butyl rubber the plasticization required for lowtemperature performance results in nullifying a major portion of theinherent ozone resistance of the polymer itself, and accordingly theantiozonants of the present invention are useful in such neoprene andButyl stocks.

These various elastomer samples were cured at about 1000 p.s.i. in asteam heated press at 285 F. with curing times adjusted in the rangefrom 30 to 120 minutes, as required to obtain optimum tensile propertiesfor each specific compound. Samples of each of the cured stocks wereheat-aged for 24 to 48 hours at 100 C. and were then subjected to ozoneexposures in both dynamic and static tests. The aging procedure employedwas the test tube method designated as ASTM method D-865-54-T.

The examples in the tables herein are limited to sulfurcuredvulcanizates; however, sulfurless curing systems, for example withtetramethylthiuram disulfide, peroxide curing systems s-uch as withdicumyl peroxide, benzoquinone dioxime, radiation curing systems, metaloxide curing of acid elastomers as for example zinc oxide andbutadieneacrylic acid copolymers and other curing systems can be usedeffectively with elastomers containing the antiozonants and synergisticantiozoant compositions.

The dynamic ozone test was conducted on la-inch dumbbell specimens ofthe vulcanizates. The exposure to ozone was carried out in analuminum-lined ozone cabinet where the concentration of ozone wasusually held at 5015 p.p.h.m. of `air by passing 6 volumes of ozonizedair/ cabinet volume/minute. This high ozone concentration is used (25 i5p.p.h.m. is specified by ASTM test D-1l49-55T) to demonstratethegprotective effect of the antiozonants in a reasonably short time ofevalulation and to approximate the atmospheric ozone concentrationsreported at ground level under certain climatic conditions in the LosAngeles area and parts of New Mexico and Alaska. Occasionally morehighly accelerated ozone exposure tests were conducted by employin-gozone concentrations as high as 150 p.p.h.m. With such high ozoneconcentrations much shorter times are required to obtain validcomparisons of the protective action of the additives ,under test (e.g.,about 8 hours). Each sample was stretched and relaxed continuously at arate of 30 times per minute, between and 20% elongation of the totalsample (0 to 28% elongation based on the narrow portion suffering theelongation) to simulate conditions of dynamic use of the rubber. Aftereach test, usually of 40 to 70 hours duration, aspecimen taken from thecenter part of the narrow portion of the dumbbell was placed under themicroscope and the depth of the observed cracks was measured. The depthsof the deeper 50% of the observed cracks were averaged, and this averagewas designated the A value and was taken as the index of ozone attack.-With'each group of 5 to 25 experimental samples, control samplescontaining Santoilex AW were simultaneously subjected to the samedynamic ozone test, and the average crack depth A value was comparedwith the A value for the crack depths of the control samples as a basisof evaluation.

In the research on which this application has been based, it has beendemonstrated that where antiozone protection is obtained in the dynamictests, protection is also afforded in static use. The static tests runon both' heat-aged and unaged samples showed this to be true withoutexception. (The converse is not always true, e.g., some staticprotection is afforded by paratiin and microcrystailine waxes, which arevalueless for protection of rubber articles subjected to dynamicusages). Specimens for static testing were mounted in` accordance withASTM procedure D-51844, method B. The mounted samples were placed in theozone exposure cabinet Wherein the ozone concentration was held at aconcentration of 25i5 plp.h.m. or 5015 p.p.h.rn. at a temperature of 40C. In this static test the samples were observed periodically and thetime was measured to the appearance of the irst crack. Since such statictest data are merely conrmative of data obtained dynamically, staticozone exposure tests for the antiozonants of the present application areomitted herefrom for the sake of brevity. It suflices to state that longcontinued tests show that where virtual inmunity against ozone wasobtained with an antiozonant or a synergistic antiozonant composition ina 70-hour test at 25i5 p.p.h.m. of ozone or a iO-hour test at 50i5p.p.h.m. of ozone, static protection of 3 months to one year wasobtained at ozone concentrations oif 50 p.`p.h.m. without failure of thesamples. The Santoflex AW controls (2 pts. Santoex AW) showed severecracking in the 70-hour test and failed in about 100 hours or less underthe same static test conditions.

Similarly mounted panels of specimens (ASTM procedure D-518-44) werealso statically tested in outdoor weather experiments in Florida(Miami), California (Los Angeles), and Michigan (Detroit). InCalifornia, where highest concentrations of ozone occurred over the timeof the test (varied from 5 to 60 p.p.h.m. dependent on weathervariations), up to six mounths of outdoor exposure were required todevelop cracks (ASTM rating 4) in the samples containing antiozonants orsynergistic antiozonant compositions. The Santofiex AW controls not onlycracked but failed in a month under simultaneous exposure. In theFlorida and Michigan tests the protected samples .did not crack in aone-year test whereas the control samples not only cracked but failed inthe same test. The rating method for the static exposure tests is shownby the following tabulation:

Rating Development of static tests N o development of any kind.Microscopic cracking.

Fine visible cracking. Pronouuced visible cracking. Severe visiblecracking.

, rubber compound to accelerate vulcanization of the compound duringprocessing (e.g., during milling, extruding, etc.) prior to theconventional curing step. If an additive is too scorchy the compoundcures to such a degree that it cannot be moldor press-cured to intendedusefull end items. Scorchiness, although often correctedl by use of cureretarders, low sulfur and low-accelerator recipes, is not desirable inany type of rubber additive, and accordingly an ASTM method, alreadyestablished to measure scorch, was em-ployed to evaluate theantiozonants of the present invention with respect to scorchiness.

The scorch time is deiined as the number of minutes required as measuredfrom the start of the test, for the rubber compound to increase aspecified number of points in viscosity (on a Mooney viscometer scale)above the minimum viscosity lrecorded when operating the Mooneyviscometer at a xed temperature selected preferably in the range of 250-to 300 F. In .the present tests five points in viscosity was used asthe specified number of viscosity points, and the temperature of testwas set at 250 F.; these specifications were selected in accord with themost generally reported practice in the tire manufacturing industry. A20 minute scorch time is considered a minimum for tire stocks with 22 to25 minutes or more being preferred by industry.

Discoloration tendency and stain and migration of the antiozonants ofthis invention were measured in accordance with ASTM procedure D-l14855and D-925-55 respectively, and also a modication of the last methodemploying white natural rubber stock strips in place of the whitepainted panels of the unmodiiied D-925-55B. This discoloration tendencyof elastomer additives is important where light colored elastomercompounds are desired, e.g. for white sidewall tires, seals and gasketsfor white enamel articles such as refrigerator doors, white instrumentpanels, etc, Thus, antiozonants should be non-staining signifying thatthey will not resul-t in discoloration of white products which eitherincorporate the said antiozonants r are in contact with compoundsincorporating them.

The tendency to discolor white articles was measured in this work bypainting a compound containing the antiozonant with a white paint andexposing the sample to a sunlamp for 24 hours. The lamp, temperature oftest, type of paint, rating of samples, etc., were as specified in saidASTM method D-ll48-55. The ratings employed in the staining anddiscoloring tests were as follows:

Very' dark Dark Medium Light Very light ing was measured according toASTM D-925-55 using the specied light source. taining antiozonants ofthe present invention were contacted with white enamel-coated panels,and also with squares of white natural rubber stock designed lfor whitesidewalled tires. These panel-rubber and white rubber- The elastomersamples con-l experimental samples were exposed to the sunlamp for 24hours, and the contacted white surface was observed to detect stain fromthe antiozonant, and to detect any migration outward from the `area ofdirect contact with the experimental sample. Ratings for stain were thesame as for the discoloration test (see above), while migration wasnoted asrmuch, medium, little, very little, or none.

SYNERGISM tion comprises the discoveries of antiozonant compositionswhich rely on the action of synergistic antioxidants, parain and/ormicro-crystalline waxes in combination With specific derivatives ofp-phenylenediamines of the present invention in which there are fourhydrocarbon substituents on the amino .nitrogens When used in more than3 parts per 100 parts of elastomer the said derivatives ofp-phenylenediamine give virtual immunity to ozone attack per se.However, in combinations with 1.5 to 6 pts. of certain antioxidants ormixtures of antioxidants it has been found that reduced amounts (eig,0.5 to 3 parts) of the said specific p-phenylenediamine derivativesserve to protect elastomers against ozone deterioration, although theantioxidants by themselves do not impart ozone resistance totheelastomer compounds, nor do the reduced amounts of said specific-diaminoderivatives alone (i.e., in the absence of the specific antioxiofprotecting elastomers and plastomers against ozone, have the property ofgreatly increasing the effectiveness olf reduced amounts o-fmy-'specitic antiozonants in elastomer and plastomer compositions. Suchantioxidants I yrefer to herein as synergists An alternativeinterpretation of my invention is that a small amount of diaminoderivative, which itself can impart ozone resistance to elastomer andplastomer compositions incorporating said derivative in certain minimumamounts can develop antiozone activity in antioxidants when admixedtherewith in less than such minimum amounts.

The mechanism of the action of such antioxidants in synergisticantiozonant composition is not entirely understood. On possibleexplanation is that the diamino antiozon-ants themselves may eitherreact with certain of the rubber compounding ingredients or may enter tosome extent into the complex vulcanization reactions in the curing ofthe elastomer compositions, and that the synergistic antioxidant and/orheavy Imetal salt and/or wax alters the degree to which the diaminoantiozonant so enters the side reaction or vulcanization reaction; orthe antioxidant may improve the migratability of the diamines. However,the exact mechanism is immaterial to the practice of the invention whichthe subsequently discussed data serve to exemplify.

It is also apparent that the Wax component is a contributory componentof some of the synergistic compositions in GR-S (Examples A-l, 2, 10,-11 and 14). Also virtual immunity resulted in an aged sample with 3parts of the N,N-dimethyl derivative of N,N-di2 octyl-p-phenylenediamineantiozonant in neoprene WHV (Examples C-18 herein) with 2.0'partsneozone A and 1.5 pts. wax (Atlantic 1.115); whereas with the sameamounts of the antiozonant and neozone A but with no wax virtualimmunity was not attained (Example C47). Data showing the synergisticeffect of wax with other antiozonants of the present invention whilesimilar have been omitted for the sake of brevity.

I have found that while parailin and mi'crocrystalline wax andcombinations thereof per se give some protection -to static samples ofvulcanized elastomers no protection is afforded vulcanized elastomers indynamic usage. My findings confirm John O. Cole. In G. S. Whitbystreatise entitled Synthetic Rubber, published in 1954 by John Wiley andSons, Inc., New York City, on page 541, Mr. Cole states, It should bepointed out that, under dynamic flexing, wax offers no protection toeither GR-S or natural rubber from the deterioration by ozone.

In contrast to this fact I have shown that waxes when used with theantiozonants of this invention can act synergistically, that is, canenhance the protective value of the antiozonants.

Example A-14 in'compan'son with A-ll shows the beneficial synergisticetect of a heavy metal soap, a salt of a fatty acid. (The GR-S 11605test com-pounds used in these two examples were found to be similar inozone dants) show adequate vprotection of the elastomer compounds. vSuchadmixed and/or interacted components resistance to GR-S `1500 compounds(compare with Example A-5).) The GR-S 1605 compound contains elastomeridentical with that of AGR--S1500 'and 1600 compounds and differs fromthem in that (l) it contains a medium abrasion furnace black (PhilblackA added at the polymer plant instead of the high abrasion furnace black,Philblack O), and (2) it contains Polygard (about 1 part) added at thepolymer plant, a non-staining antioxidant, instead of the PBNA orBLE-25, staining antioxidants added to GR-S 1500 and 1'600 at thepolymer plant. It was also demonstrated (see below lunder FurtherDiscussion of Results) that Polygard, BLE-25 and PBNA are less activesynergistic antioxidants and compounds containing' such antioxidants ata level less than 1.5 parts/ 100 parts elastomer can be used to obtain jcomparative evaluations of antiozonant compositions therein. e*

It has been further demonstratedthat similar but not 15 identicalbeneficial synergistic effects 'are obtained with antiozonant diaminesof the present invention by com bi1-lation with other heavy metal soapswherein the acid component is derived from fatty acids (from 3 to 19Table III), and (4) age resistance. Age' resistance, not exemplified inthe tables, was evidenced by better retention of tensile strength andelongation after aging 72 hours at 100 C. in the test tube method (ASTMmethod carbon atoms) naphthenic acids (from I6 to 20 carbon 5 D-86554-T)then shown by compounds prepared with atoms) or rosin acids,disproportionated rosin acids, 3 partsof either individual antiozonant.hydrogenated rosin acids, or the like, and wherein the heavy metal istin, lead, manganese, cobalt, nickel or OBSERVED RESULTS iron. The datafor such synergistic compositions, de- Table I shows data for thedimethylated antiozonants tails of which are omitted herefrom for thesake of brevity, 10 of this irlVontion in Comparison With non'mothylatodpar' demonstrated that, in the absence of synergistic antioxiont di(soC- and tort-octyl)-P-Phnylonodiammos in S61 dants (other than theinsignificant amounts present from oral oiastomors sublootod to thodynamic ozono exposure the polymer plant) 2 parts of diamineantiozonants of test. GR-S and natural rubber samples containingSantothe present invention can give virtual immunity to the lloX AW Woretostod Simultaneously With oaoil group ro' aged elastomer compounds when1 to 2 parts of such 15 SPootiVolY of GR-S 1500 and natural rubbersamples heavy metal salt are wmbined therewith, when COUP containing theamino compounds of the present invention bined with 2 to 5 parts ofappropriate synergistic ami to monitor the procedure `and to giveassurance that the Qxidams together with 1 to 2 parts 0f the heavy metalseveral results were valid for evaluating the relative efsalts, aslittle as 0.5 to 1.5 pts. of the diamine antiozo. fectiveness oftheseveral amino compounds for protection nants of the present inventionare adequate to attain of tho several olastomers against ozonoattaoklSanfovirtual immunity for the aged elastomer compound. flax AWsiloWs no Protective action against ozono for In addition to synergismdemonstrated herein for an- HYCar 1014, neoprene and Butyl rubber andaccordingly tioXidant-antiozonant admixtures, it has aiso been found Wasnot incorporated into the Control Compounds thereof. advantageous tocombine one or more different anti- Ortho* and mota-diamino aromaticcompounds are ozonants of this invention with one or more antiozonantsrelativo-ly maCtIVo as antOZonarltS, also Certain Comof otherinventions, e.g., those taken from U.S. Patent Pounds, such asPllonYbalPhanaPhtbB/lamino, (li-bola- 2,705,224. In Example B 1 1 partof N,N'di2octy1 naphfhylamine, .hydronaphihylamine derivatives, a1-NN'.dimethyppphenylenediamne combined with 2 though good annoxidants arenot good antiozonants. parts of N,N'-tetraisobutylpphenylenediamineshows It should also be Called to attention that the `GR-S unexpectedimprovements over either individual additive 1500 oXamPlos of Table 1Contained about 1-25 Parts of in (l) protection of polymers againstozone (Examples either phenyl-bota-naphthylamine (PENA) or a diPlleIlYl-B-2 and -3), (2) anti-Scorch tendency (see examples of amine-acetonecondensation product (BLE-25) in addi- Table. II), (3) anti-stainingtendency (see examples of tion to the other additives shown.

Table] ELASTOMERS CONTAINING ANTIOZONANTS OF THE PRESENT INVENTION[Accelerated dynamic exposure: ozone at 5015 p.p.h.m,; 40 hrs.; 40 C.;30 flexures/mirn] "A Value crack Pt depth (microns) s. Example SampleElastomer Pts. Additives* wax p Aged 24 Uuaged hours at GROUP A 5 N,Ndimethy1-NN'dl2octyl-p-phenylenediamlne l. 0 0 0 5 dn 0 5 10 3 do 0 25 803 do 1. 5 70 2 do 1,5 90 125 2 N,N dimethyl N,N'd1(1 ethyl 3methylpentyl) p 0 85 65 phenylenediamine. 3 d0 0 55 40 3N,Ndi-2-octy1-p-pheuylenediamine 0 50 80' 3N,Ndi(1ethyl-3-methylpeutyl)-p-phenylenediamine 0 45 100 2N,N-dimethyl-N,Ndi-2-octyl-p-phenylenediamine 0 110 120 2 dn 1.5 100 1102 N ,N, dimethyl N,N d(1 ethyl 3 methylpentyl) p 0 130 120phenylenediamine. 2 Santoex AW 1.5 200 30G 2N,NdimethylN,N-di-2octylp-pheuylenediamue plus 1 1. 5 70 20 partstannous stearato. l

1 Z- d n 1 N ,N -dlAmethyl-N,N -di2octyl-p-phenyleuediamine plus 2 0 10050 pts. l\ ,Ntetraisobutyl-p-phenylenedamine. 2. Control t dn 3N,N-tetraisobutyLp-phenylenediamne 0 130 150 3. Z7 do 1N,Ndmethyl-N,Ndi-2-octyl-p-phenylenediamine 0 300 250 4 Control 2 do 8 N,Ndimethyl-N ,N'-d(2ethylhexyl) -p-phenylened 0 85 110 5, dn 2 rin 5 rin0 70 95 6 :1n l dn 3 N,N'd1(2ethy1hexyl)-p-phenylenediamine 0 70 130 7-.do 2- -dn 5 n 0 40 55 8. P-QEL. do 5 Oxailte ofN,N-dimethyl-N,Ndi-2oetylp-phenylened1 1. 5 50 v 100 m e. 9. P- dn 3 N,N' dimethyl N,N' di(1,1,3,3 tetramethylbutyl) p 0 110 120phenylenediamne. 10 Controldn 2 Santoiex AW 1. 5 190 280 GROUP c 1BIP-36 Natural rubber. 3 N ,Nvdimethyl-N ,Ndi-2-octyI-p-phenylenediamlne0 65 130 2 IBF-37 n 3 dn 1. 5 55 100 8 BF-SS dn 3 N,N dimethyl N ,N di(1ethyl 3 methylpentyl) p 0 75 80 phenylenediamine. v

Table I-Continued ELASTOMERS CONTAINING ANTIOZONANTS OF THE PRESENTINVENTION [Accelerated dynamic exposure: ozone at 50 I5 p.p.h.m; 40hrs.; 40 C.; 30 flexures/min-] A Value crack depth (microns) Pts.Example Sample Elastomer Pts. Additives* wax Aged 24 Unaged hours at 4BIT-39 rln 3 rln 1.5 55 80 BF-40-Control 3. do 3N,N-dimethyl-N,Ndi(2-ethylhexyl)p-phenylenediamine 0 60 6- BF-4l dn 3do 1. 5 50 l5() do 3 N,Ndi2oetylpphenylenediamine 0 40 270 rlo 3N,Nd.i(1-etl1yl-3-methylpentyl)-p-phenylenediamine 0 55 190 dn 5 do 1. 525 40 do 5 Santollex AW- 0 85 145 -do 5 dn 1.5 325 445 Hycr 1014 5N,l\lddimethyl-N,N'-di-2-octyl-pphenylenedlamine g gg 50 o 3 o do 3 N,Ndimethyl N,N' di (1 ethyl- 3 methylpentyl) p 0 140 150 phenylenediamine.do 3 N,NdimethylN,N-di(Z-ethylhexyl)-p-phenylenediamine.. 0 75 ---.doNone (1.5 pts. BLE-25 only) 0 700 600 Neoprene WHV. N ,l\lddimethyl-N,N'd.i2octylp-phenylenedlarmne (1) 5 7g 85 o o fin None o 28o 34g Butylrubber-.-- 3 N ,N '-dimethylN,Ndi-2octyl-p-phenylenediamine 0 50 50 doNone 0 100 -80 *Natural rubber samples contained 1 pt. PBNA antioxidant;Hycar 1014 contained 1.5 pts. BLE-25 antioxidant, and Neoprene WHVcontained 2 pts. Neozone A antioxidant.

i For comparison with other group A examples. 2 Primary alkylderivatives for comparison 1:with

antiozonants of this invention.

3 Examples containing primary octyl derivatives for comparison withantiozonants of this invention.

The ozone cracking in the case of the Santoilex AW controls for GR-S andnatural rubber as well as the neoprene, Hycar and Butyl controls wasgreatly in excess of the 50 microns A value which represents virtualimmunity to ozone attack, while the elastomers compounded withappropriate amounts of the antiozonants of the present invention arebetter than the controls and generally approach or are within the rangeof that criterion of A value.

In further comparative studies other new compositions more effectivethan Santoliex AW for protection of elastomers were discovered whichalso are represented by the formula R(CH3)N-R'-N(CH3)R", in which R isp,p'biphenylene, methylenediphenylene, or p,piminodi phenylene and oneor both of R and R" are secor tertalkyl groups containing S to 12carbons. Thus derivatives of the N,Ndioctyl parent Iantiozonants whereinthe hydrogens of the amino groups of the just mentioned antiozonants aresubstituted by methyl groups, are examples of the present newantiozonants for protection of various elastomers.

Data for speciments prepared from hot GR-S (GR-S 1002) were very similarto those for cold GR-S set forth in Table I and have therefrom beenomitted for the sake of brevity.

In similar compounds the antiozonants of the present invention protectelastomers of various other types against ozone. Thus data for protectedand unprotected polybutadiene, Philprene and BD/S/AA (butadiene/styrene/acrylic acid terpolymer), further demonstrate the high effectiveness ofthe new antiozonants, several of which are exemplified in Table l. Datafor the dynamic test of typical antiozonants of the present inventionare exemplified in FIGURE l for the range of 0 to 5 parts antiozonantsin GR-S 1500.

Wax synergism with the new antiozonants is demonstrated by Examples A-l,2, 10, -ll, C-6, C-9 and -17. Synergism obtained with other antioxidantsin GR-S 1500 in combination with an antiozonant or this invention isillustrated by B-l, and synergism with a heavy metal soap, by A-l4.While data of the same type have been obtained for the other newantiozonants per se and in various synergistic combinations in variouselastomers, such similar data although not identical are omitted hereinfor the sake of brevity since they are merely confirmatory of thesedisclosures.

^ A series of elastomer compounds was prepared which conclusivelyestablished that the synergistic action with the antiozonants of PENA(phenyl-beta-naphthylamiue) and BLE-25 (acetone-diphenylaminecondensation prod-` uct) in the small quantities commonly introduced atthe GR-S rubber plants in relatively insignificant, and that the databased on compositions including commercial GR-S afford a valid basis forevaluation of the antiozonants per se, as `well as in synergisticcombinations with other more active synergistic antioxidants and/orwithv significant quantities of P'BNA and/or BLE-25.

ln FIGURE 2 dynamic ozone exposure data are shown delineating thelimitations on the carbon count of the hydrocarbon substituted diamineswherein R is a monophenylene nucleus, unsubstituted or hydrocarbonsubstituted, and R and R are secor tertoctyl groups. Such curves arealso the bases for the similar limitations of the antiozonants of thisinvention (l) wherein R and R" are secor tert-C9 to C12 alkyl groups andalso (2) wherein R is a diphenylene nucleus, both unsubstituted andhydrocarbon substituted, and wherein R and R are secor tert-octyl,nonyl, decyl, undecyl or dodecyl groups, but are omitted' herefrom forthe sake of brevity. The interpretation of FIGURE 2` has been consideredmore fully hereinbefore.

In static samples it has been demonstrated that the' addition of from lto 5 parts of the new antiozonants of this invention increases the timepreceding appearance of the first ozone cracks as muchas 10G-fold. overthe` time of appearance of first cracks in the synthetic rubber controlscontaining Santoilex AW. Static data being merely confirmatoryand'cumulative of the/.effects herein- Examples of Table l demonstratethatfin the anti-l ozonants of this invention substituent methylVradicals accesos ozone tests and for outdoor weathering tests confirmthe dynamic test results with regard to the antiozonant compositions ofthe present invention, but as such tests are less stringent than thedynamic test and as such data' are only cumulative they have beenomitted herefrom for brevity.

`Data of Table Il herein exemplified improvement of the scorch time ofthe GRS evaluation compound containing the new experimental antiozonantsin comparison with control GR-S 1500 samples. Example containing 3 pts.of the parent diamine, N,Ndi2-octyl-p-phenylenediamine, showed a scorchtime of 20 minutes (Example 4). The dimethylated derivative of .thiscompound, an antiozonant of this invention, in Example II-6 showed 30minutes scorch time. The improvement in Scorch time, realized in everyVcase for the new antiozonants of this invention including the N,Ndi(secand tertnonyl) to N,N-di(sec ortert-dodecyl)-(inclusive)-p-phenylenediamines in comparison with theparent N,Ndi(secor tert-alkyD-p-phenylene diamines, is amplydemonstrated by the data obtained, and further data are omitted herefromfor the sake of brevity.

The improvement in staining and migration tendency of theN,N-dimethylated derivatives (of the present invention) of the parentN,Ndi(secand tert-alkyl) substituted diamines is illustrated by the dataof Table III. As in the case of the scorch tendency, the N,N-dimethylderivatives of the present invention) of the parent N,N'- di(sec andtert-alkyl)-p-phenylenediamine in every case showed less stain than theparent compounds. The new compounds show light to very light stain o-rcoloration in every case. The order of improvement is demonstrated amplyby the data of Table III so that further data are omitted herefrorn inthe interest of brevity.

Table I1 SCORCH TIMES MEASURED AS MINUTES IN MOONEY VISCOMETER AT 250 F.TO INCREASE OF 5 POINTS IN VISCOSITY ABOVE THE MINIMUM VISCOSITY (ASTMMETHOD D-1077-55-T), GRf-S 1500 COM- POUNDS IVITH 1.5 PTS. W'AX ExampleScotch No. Pts. Additives time. min.

1. Control-. N ,N di 2 ethylhexyl p phenylene 2G diamine 2 5 N,N-dlmetliy1-N,N' di (2-ethylhexyl) 30 p-phenylenediamine 3. Control.- 2N,N-di-2-0ctyl-p-phenylenediamine 22 4. Control-. 3N,N-di-2-octyl-p-phenylen ediamine 20 5 2 N ,N,dimethyl N, N di 2 octylp 31 phenylenediamine 6 3 N,N dimethyl N, N di 2 oet-yl p 30phenylenediamine 2 N, N' di (1 ethyl- 3 methylpentyl) 30 pphenylenediamine 3 N, N di (l ethyl 3 methylpentyl) 27p-phenylenediamine 2 N, N dimethyl- N, N di (1 ethyl- 3 '43 methylpentyl)pphenylenediamine 3 N,Ndimethyl-N,Ndi(1-etl1yl3 44methylpentyl)-p-phenylenediamine 11. Control. 3 Mono-oxalate oi N, N di2 octyl p 33 phenylenediamine 12. Control. 3 Mono oxalate of N, N di (1ethyl 3 43 methylpentyl) p phenylenediamine 13 3 Mono oxalate oi N, N'dimethyl N, 34

N di 2 octyl p phenylenediamine 14 3 Mono oxaiate of N, N dimethyl N, 45

N' di (l ethyl 3 methylpentyl) p-phenylenediamine 15 3 Mixture oi 1 partN, N dimethyl N, 35

N di 2 oetyl p plienylenediamine and 2 parts N, N' tetraisobutyl pphenylene-diamine 16. Control 1 3 N,Ntetraisobutyl p-phenylenediamine 34l For comparison with Examples 6 and 15.

2i) T able III IMPROVEMENT IN STAINING AND MIGRATION CHAR- ACTERISTICSOF ANTIOZONANTS PREPARED BY ALKYLATION OF PARENT DIAMINE COMPOUNDS OFTHE PRESENT INVENTION IN GR-Si 1502 ELAS- TOLIER(ASTM METHOD D-1148-55AND D-925-55) Sample Pts. Antiozonant Stain Migration Control 1. 2

N, N di 2 octyl p Light brown. None.

amine.

N, N dimethyl N, N di (1, 1, 3, 3 tetramethylbutyl) p phenylene diamineMixture of 1 pt N, N dimethy1-N,N-di2 oetyl p phenylenediamine and 2 ptsN, N tetraisobutyl p phenylenediamine N, N' tetraisobutyl pphenylene-diamine Light grey.

Control 2 2 Dark brown- Much.

2 2 Lavender. None;

Control 3. 2 Grey Little.

Light grey. None.

Very light ETBY Control 1 Light grey-.. Very little.

l For comparison with Samples 1 and 4. *Contains about 1 part ofPolygard as non-staining antioxidant added at the polymer plant. y

FURTHER DISCUSSION OF RESULTS Part I of this invention disclosed newantiozonants which per se in rubber containing insignificant amounts ofantioxidants can protect elastomers against ozone cracking. Part IIdisclosed synergistic combinations o the antiozonants of Part I withantioxidants and/or waxes.

I have found that the quality of antioxidant required to obtain thesynergism varies with the antioxidants used. Most of the synergisticcombinations of antiozonants of Part I of this invention in combinationwith antioxidants such as thoseexamples of Table A contained at leastone part PBNA (added at the GR-S polymerization plants) in addition tothe added antioxidants.

From the data obtained in dynamic ozone tests it appeered that ll of theantioxidants of Table A used only in 2 parts per 100 parts elastomer incombination with less than 3 parts antiozonants of the present inventionper l0() parts elastomer do not quite attain effective protection inGR-S 1500 compounds, viz:

BLE-25 Antioxidant 2246 Diphenylamine Dipropylene glycol mon- PBNAosalicylate ester Rosinamine D Neozone Flectol H Parazonel-naphthyiamine Polygard But it was noted from additional data thatthese l1 less actively synergistic antioxidants, when augmented by the1.25 parts of antioxidant present in commercial Gi-S, did give eiiectivesynergistic protection of the elastomer with less than 3 parts ofantiozonant (similar to Example B-l above noted wherein 1 pt. ofantiozonant of the present invention is combined with 2 pts. of atetra-primary-alltyl-substituted p-phenylenediamine).

It is accordingly shown that to attain good synergistic activity withthose less actively synergistic antioxidants, it is necessary to employincreased quantities` thereof, or some other synergist therewith.

With respect to the antiozonants of this invention, the comment asregards the insigniiicance of less than 1.5 parts total of antioxidants(that show significant synergism when used in greater than such amount)apply. The fact that parain wax alone is a better synergist thanmicrophenylenediarnine crystalline wax has also been demonstrated. Thedata obtained with antiozonants of the present invention show theeffectiveness of the antiozonant per se, and the synergism therewith ofwaxes. In this connection, it will be noted that (1) the eiectiveness ofwax as a synergist is developed to a major extent at a wax content ofabout 1.5 parts wax with varying amounts of the antiozonant and (2) theimprovement in the aged samples from the inclusion of Wax with theantiozonant generally parallel those in the unaged samples.

It has been further demonstrated that the beneficial eiect of wax inoutdoor static tests is obtained. Thus in static usages even in theabsence of synergistic antioxidants, the time to -irst cracking of GR-Ssamples containing 2.5 parts of the new antiozonants can be especiallyincreased by inclusion of 1.5 parts wax.

The categories or antiozonants of the present invention are representedby the formula wherein R' is an arylene radical selected from the groupcomprising phenylene and diphenylene radicals and hydrocarbonsubstituted phenylene and diphenylene radicals R and R" are alkylradicals selected from the group comprising secondary and tertiaryoctyl, nonyl, decyl, undecyl and dodecyl radicals, and wherein the totalnurnber of carbon atoms in the hydrocarbon nucleus plus substitutents isfrom 24 to 37.

The data also demonstrate the application of the present invention toelastomers other than hot and cold GR-S. Natural rubber, polybutadiene,butadiene-methylvinylpyridine copolmer, butadiene-styrene-methacrylicacid copolymers and Hycar N-rubber have been successfully protectedagainst ozone by synergistic antiozonant compositions of the presentinvention.

In summarizing the parts of this invention it has been demonstratedthat: (l) the new antiozonants when used in from 1 to 5 parts in 10Gparts elastomer protect the elastomer compound against ozone attack; (2)when the antiozonants of (l) are mutually combined or are combined withantiozonants of said copending applications, or are combined withappropriate quantities of antioxidants of the several classes ofantioxidants and/ or waxes, synergistic antiozonant compositions areformed wherein reduced amounts of antiozonants will serve to protectelastomer compositions.

The appropriate incorporation of the new antiozonant compositions, i.e.,combinations of the substituted phenylenediamines with aminoantioxidants, and/or waxes (and/ or metal salts such as certain metalfatty acid salts gives virtual immunity against much higher thanordinary atmospheric concentrations of ozone, to elastomer compositions,even when the same have been subjected to radical heat-aging, thusshowing that these antiozonant combinations are capable of protectingthe products for long periods of time under dynamic as Well as staticconditions and at elevated temperatures.

The invention has further shown that when the total carbons of thecompounds are kept within designated ranges the antiozonants are highlyeiective in aged stocks, it being thus shown that the ranges arecritical I for the protection of products subjected to high temperatureresulting from dynamic usage or otherwise, but may be broadened to someextent (c g., a carbon count of say eight carbons less than theheat-aged ranges) and still be suitable for protection of static goodsnot subject to elevated temperatures or dynamic usages.

Comparison of the results attained, mutually and with the controls,shows that various synthetic elastomers are protected against ozone byincorporationof three to ve parts of the antiozonants therein; and thesame considerations show that natural rubber is similarly protected, aswell as polyisoprene prepared synthetically by emulsion polymerizationprocesses, by alkali metal polymerization (e.g., Coral rubber ofFirestone Tire & Rubber Co.), by organo-metal alkali catalysts (e.g.,the Aliin type of catalyst) or by metal yalkyl catalysts (eg, aluminumtrialkyl, lead tetraethyl and combinations of organo-metallic compoundswith metal salts).

In addition to the examples given in the tables, copolymers of styreneand butadiene were prepared which contained small amounts ofcopolymerized carbonyl-containing monomers such as methylvinyl ketone,crotonaldehyde or methylisopropenyl ketone and compounded with theantiozonants of this invention, and the results showed that theseantiozonants are useful as additives for these carbonyl-containingelastomers.

These and other elastomers may be employed as additives, eg.,plasticizers for plastomer products, for which polar elastomers areusually selected. In such cases ozone deterioration of the elastomercomponent is prevented by the antiozonants of this invention.

The samples shown in the tables cover the principal types of elastomers,above described, but the range of polymers and combinations protectedagainst ozone attack by the present antiozonants is not limited thereto,as similar protection has been obtained with plastomer cornpositionscontaining elastomers (e.g., Butyl rubber, neoprene, polybutadiene,GR-S, acrylonitrile rubber, etc), which per se show less susceptibilityto ozone attack than for example, GR-S copolymers.

Butyl rubber is known to be less susceptible to ozone attack than areGR-S elastomers. However, ozone cracking of butyl vulcanizates is anindustrial problem for certain uses as evidenced by the study of D. C.Edwards and E. B. Storey, Transactions of the Institution of the RubberIndustry, pp. 45-69, vol. 31, No. 2, April 1955. I have found Butylrubber when plasticized with oils as commercially practiced to beconsiderably attacked by ozone. I have demonstrated that theantiozonants and synergistic antiozonant compositions of the presentinvention when appropriately compounded into Butyl rubber are capable ofprotecting the resultant Butyl vulcanizates against ozone attack. Inlike manner plasticizedv neoprene compounds are protected against o-zoneattack by appropriate use of antiozonants and antiozonant cornpositionsof the present invention.

Variations in compounding of the elastomers can nullify the protectiveaction of these antiozonants. For example, high amounts of waxes,plasticizers (particularly cils containing unsaturates, such as ParaFlux2016 and Bardol), zinc stearate, rosin acids or stearic acid lower theeffectiveness of our new additives in rubbers. Caution should beexercised by the compounder t0 avoid excessive amounts of suchingredients particularly where the elastomer is subjected to dynamic use(i.e., in amounts greater than one mole per mole of diamine antiozonantincorporated).

In general from 1 to 3 parts of the new diamine antiozonant per ofrubber in the absence of added antioxidants is adequate for practice ofthe present invention in protection of statically employed items(prepared from natural and synthetic rubbers) for practical periods oftime against deterioration duc to ozone attack; 3 or more parts arepreferred for elastomer items in dynamic usages. In synergisticcombinations, however, from 0.5 to 3 parts of the tetra-substitutedp-phenylenediamines, tetra-substituted benzidines, tetra-substitutedbis(aminophenyl)- amines, and tetra-substituted bis(4aminophenyl)methands of this invention are suicient to provide ozone protection forthe elastomer compounds for both static and dynamic usage.

The amount of antiozonant compositions containing synergisticantioxidants and/or waxes required to give ozone protection toelastomers varies with the type of antioxidants and metal salts employedand depends at least in part on whether the antioxidants and metal saltsare used in combination or singly; in general for the practice of thepresent invention the total amount of synergistic additives varies from1.25 to 6 parts per 100 of elastomer. While the use of small amounts ofwaxes in rubber compounds together with antioxidants is recognized inthe prior art, the appropriate combination of waxes with theantiozonants of the present invention, both with and without synergisticantioxidants to develop synergistic antiozonant compositions,constitutes an unforseeable and a valuable advance in the protection ofelastomer and plastomer compositions against ozone cracking, in view ofthe fact that waxes were heretofore considered to be harmful for ozoneresistance of elastomers in dynamic usage.

The antiozonants and synergistic antiozonant compositions of the presentinvention have also been yfound to be efecti-ve in protection againstozone cracking of plastomers which have residual unsaturation or activehydrogens such as may be present in methylene or methinyl groups. Thusresins or plastomer compositions comprising polymers and copolymers ofvinylchloride, vinylacetate, alkylacrylates, etc., in combination withunsaturated polymer ingredients, are subject to attack by ozone, andsuch attack is avoided when the new antiozonants are present in suchcompositions.

It has further been demonstrated that the new antiozonants andsynergistic antiozonant compositions can be compounded with the GR-S1500 in the Banbury mixer, on the rubber mill, or by incorporation inthe elastomer latices as above described either at the polymer plant orby the consumer at any time prior to coagulation and drying. Theadditives of the present invention may be incorporated as fatty acidsalts, and also salts of dibasic acids such as oxalic, maleic, and thelike, without departing from the practice of this invention (examples ofTable I and Table II).

The research has shown that the new compounds are valuable antiozonantsof improved staining characteristics for plastomers and resins as wellas for natural and synthetic rubbers and are particularly usefulantiozonants for tires and similar natural and synthetic products(subject to ozone attack) which require relative long Scorch times andwhich attain high operating temperatures, such as those temperaturesattained by heavy duty truck tires, and such temperatures may even riseto above 300 F. in use. Antiozonants are herein deiined as additiveagents which protect the polymeric material, eg., natural and syntheticrubbers, against deterioration due to ozone attack. While serving asantiozonants the new compositions also serve as antioxidants, i.e., thenew products of this invention protect against deterioration of tensileproperties of rubber compounds due to attack by oxygen and sunlight.However, the antiozonants must not be too reactive with oxygen or theycan too rapidly disappear from the compounds incorporating them andozone protection will thereafter be absent. The present classes ofcompounds represented by R(CH3)N-R-N(CH3)R as well as each synergisticcomposition described herein is specic and `differs in general fromother amines such as diarylamines, arylenediamines, and theirderivatives and mixtures with other types of antioxidants in that othermembers of these general categories and their mixtures will noteffectively protect against attack by ozone.

These new antiozonant compositions have also been found eifective inprotection of elastomer dispersions such as latices of natural rubber,GR-S elastomer, neoprene, acrylonitrile copolymeric elastomers, and thelike which are to be used for coating and nlm-forming purposes, eg., forpaper coating, wall paints, etc. By incorporation of the new antiozonantcompositions in the latices together with the vulcanizing ingredients,the subsequently formed cured films therefrom are elfectively protectedagainst ozone cracking.

An antiozonant composition as used herein denotes any of the amineantiozonants represented by as herein defined, as well as each and everysynergistic composition described in the preceding discussion whethercontaining one or more of each class of synergists described, i.e.,waxes, certain metal salts, and the designated classes of antioxidants.

Herein the term elastomer is employed to designate an elastic polymer ormacromolecule, whether a naturallyoccurring material or a Syntheticpolymeric substance. Plastomer 4is deiined as including both thermosetand thermoplastic high-molecular weight resinous and plastic materials.These definitions follow those used by Harry L. Fisher, Industrial andEngineering Chemistry, vol. 31, p. 942 (1939).

While there have been described herein what are at present consideredpreferred embodiments of the invention, it will be obvious to thoseskilled in the art that minor modications and changes may be madewithout departing from the essence of the invention. It is therefore tobe understood that the exemplary embodiments are illustrative and notrestrictive of the invention, the scope of which is dened in theappended claims, and all modicati-ons that come within the meaning andrange of equivalency of the claims are intended to be included therein.

I claim:

1. A sulfur vulcanizable rubber normally subject to cracking containing,in suicient amount to retard said cracking, an antiozonaut compositionessentially comprising a p-phenylene diamine having attached to each ofits nitrogen atoms a methyl groupr and a tertiary alkyl group containingfrom 8 to 12 ,carbon atoms.

2. A sulfur vulcanizable rubber normally subject to cracking containingan antiozonant composition essentially comprising N,N' -dimethyl-N,Ndi(tertoctyl)p phenylene diamine in suiiicient amount to retard itscracking.

3. A sulfur vulcanizable rubber normally subject to cracking, containingan antiozonant composition essentially comprising N,N' dimethyl-N,Ndi(1,1,3,3tetra methylbutyl)-p-phenylenediamine.

References Cited in the le of this patent UNITED STATES PATENTS2,115,473 Semon Apr. 26, 1938 2,323,313 Dennstedt July 6, 1943 2,395,382Walters Feb. 19, 1946 2,451,642. Watson Oct. 19, 1948 2,615,919 BiswellOct. 28, 1952 2,781,330 Downey Feb. 12, 1957 2,822,396 Dent Feb. 4, 19582,883,362 Rosenwald et al Apr. 21, 1959 OTHER REFERENCES 'Shaw et al.:Rubber World, vol. 130, August 1954, pp. 636-42.

1. A SULFUR VULCANIZABLE RUBBER NORMALLY SUBJECT TO CRACKING CONTAINING,IN SUFFICIENT AMOUNT TO RETARD SAID CRACKING, AN ANTIOZONANT COMPOSITIONESSENTIALLY COMPRISING A P-PHENYLENE DIAMINE HAVING ATTACHED TO EACH OFITS NITROGEN ATOMS A METHYL GROUP AND A TERTIARY ALKYL GROUP CONTAININGFROM 8 TO 12 CARBON ATOMS.